Build a Phased-Array Radar in Your Garage that Sees Through Walls

Until recently phased array radar has been very expensive, used only for military applications where the cost of survival weighs in the balance. With the advent of low-cost microwave devices and unconventional architecture phased array radar is now within the reach of the hobbyist and consumer electronics developer. In this post we will review the basics of phased-array radar and show examples of how to make low-cost short-range phased array radar systems — I built the one seen here in my garage! Sense more with more elements by making phase array your next radar project.

Phased array radar

In a previous post the basics of radar were described where a typical radar system is made up of a large parabolic antenna that rotates. The microwave beam projected by this antenna is swept over the horizon as it rotates. Scattered pulses from targets are displayed on a polar display known as a Plan Position Indicator (PPI).

Block diagram of a conventional radar system using a parabolic dish.

In a phased array radar (PDF) system an array of antenna elements are used instead of the dish. These elements are phase-coherent, meaning they are all phase-referenced to the same transmitter and receiver. Each element is wired in series with a phase shifter that can be adjusted arbitrarily by the radar’s control system. A beam of microwave energy is focused by applying a phase rotation to each phase shifter. This beam can be directed anywhere within the array’s field of view. To scan the beam rotate the phases of the phase shifters accordingly. Like the rotating parabolic dish, a phased array can scan the horizon but without the use of moving parts.

Simplified block diagram of a phased array radar emitting and receiving a plane wave from a point target.

To scan the entire horizon you often will need 4 or more arrays. This is why the SPY-1 radar uses 4 panels directed fore, aft, port, and starboard.

Phased array radars at short ranges

Long-range phased array radar systems focus their microwave beams in the far field using relatively simple phasing techniques to steer the beam. Most radar arrays that we might build for hobbyist or consumer applications will be operating at short ranges using low-cost wide-band microwave radar devices. At these short ranges radar targets are often in the near-field where it becomes difficult to focus the antenna beam using conventional far-field methods without accounting for wavefront curvature.

When a wave of any kind is emitted from a source it travels outwards in a spherical pattern. At long distances this sphere appears planar (e. g. a plane wave) as the spherical wave spreads out as it radiates away from the source antenna.

There are several ways to account for wavefront curvature at short-ranges. You can apply a parabolic phase function to each of your phase shifters or you can receive (or transmit) with each element independently and back-out the wavefront curvature in software. There are many ways to achieve this all of which depart from the traditional phased array architectures.

Scattering of spherical waves from a point target that is in the near-field of a phased array radar.

Unfortunately using numerous digitizers at useful bandwidths for radar continues to be prohibitively expensive for consumer products and the hobbyist when a design requires 50, 100, 1000, or 5000 elements. If you are willing to trade acquisition time for cost you could implement a much less expensive near-field array using switching techniques. In this post we’ll discuss three examples of switched-array radar systems.

In a switched array system the transmit and receive ports of one low-cost radar sensor are switched (or multiplexed) across an array of antenna elements using microwave switches. Data from each combination of transmit and receive elements is digitized and stored where focusing (or image reconstruction) is computed in the digital domain. This method can support frame rates of 10, 20, or even 40 FPS. Specific examples of this technique are shown below.

Prototype thru-wall radar

Anyone can build a switched array radar system. Here is an example of one built in my garage from 80/20 aluminum and some Mini-Circuits components. The size of the array was set by the longest 6 pieces of 80/20 I could find at the local junk yard, which were 8’3”. In this system I multiplexed the transmitter port and receiver port across 13 and 8 antennas respectively. The switching sequence allows for the phase center of this radar to be electronically moved down its length for a total of 44 effective radar Transmit/Receive pairs. I used a Synthetic Aperture Radar (SAR) algorithm that accounts for wavefront curvature to form the imagery.

Garage-built prototype of a through-wall phased-array radar system.

Block diagram of a near-field phased array radar system using antenna multiplexing.

The purpose of this radar was to prove the concept of imaging through concrete walls at stand-off ranges. It could image (by image I mean display a small red blob at a top-down view of what is on the other side of the wall) a 12 oz soda can through a 4” thick concrete wall at a stand-off range of 20′, not bad for a garage-built system.

MIT professional education/IAP array radar

Given the interest in the MIT coffee can radar course, I worked with colleagues at Lincoln Laboratory to develop a phased array course. To make the low-cost student built radar kits we added a pair of microwave switches and used a switched-array layout nearly identical to the thru-wall radar. These phased array radar devices were assembled using pegboard and WiFi antennas. The latest iteration of this radar device achieved 20 FPS. Anyone can build a phased array radar with WiFi antennas and pegboard.

Summary

Phased arrayed radar has been very expensive and is traditionally used in state-of-art air defense systems but today you can make your own at short-ranges. Try phased array radar for your next project, sense or image something fast, accurately, and without moving parts.

Author Bio

Gregory L. Charvat makes his own phased arrayed devices, is the author of Small and Short-Range Radar Systems, co-founder of Hyperfine Research Inc., Butterfly Network Inc. (both of which are 4catalyzer companies), visiting research scientist at Camera Culture Group Massachusetts Institute of Technology Media Lab, editor of the Gregory L. Charvat Series on Practical Approaches to Electrical Engineering, and guest commentator on CNN, CBS, Sky News, and others. He was a technical staff member at MIT Lincoln Laboratory where his work on through-wall radar won best paper at the 2010 MSS Tri-Services Radar Symposium and is an MIT Office of the Provost 2011 research highlight. He has taught short radar courses at MIT where his Build a Small Radar course was the top-ranked MIT professional education course in 2011 and has become widely adopted by other universities, laboratories, and private organizations. Starting at an Early Age, Greg developed numerous radar systems, rail SAR imaging sensors, phased array radar systems; holds several patents; and has developed many other sensors and radio and audio equipment. He has authored numerous publications and has received press for his work. Greg earned a Ph.D in electrical engineering in 2007, MSEE in 2003, and BSEE in 2002 from Michigan State University, and is a senior member of the IEEE where he served on the steering committee for the 2010, 2013, and 2016 IEEE International Symposium on Phased Array Systems and Technology and chaired the IEEE AP-S Boston Chapter from 2010-2011.

Based upon the slides on his website, he’s smearing 1mW of transmit power across the 2-4GHz band roughly at a sweep rate of 2.5 to 10ms, with a 20Hz pulse rate. That may put the average EIRP well below what they care about. It’s technically UWB that lets you sneak under the noise floor legally. Much to study on that one still.

If you stay in the ISM bands with the allowed EIRP then no…
If you are using the amateur radio bands, there are some details like having to transmit your callsign every now and then and of course there is a power limit¨, but way bigger then non-HAM (and you need to have the appropriate license).

Through-wall radar has seen some talk – certain US local police depts. like to use it without a search warrant and thus some people think they are violating privacy, but there has not been any civilian on civilian case (yet), so we’ll just have to wait and see…currently there are no specific rules about wall penetrating radar, the judge, however, might have a different opinion…

It is quite easy to build a Faraday cage and then feed in the bands that are required. The cost of a cage is easily going to swamp the cost of piping a repeater inside. Heck, femtocells anchored to broadband are available as well and at a very low cost.

I doubt that many would opt for the cage anyways since it could double/triple the cost of any structure. More if you want the gold-doped windows to let light in but still have the cage effectively keep snoopers out and your privacy in.

I wonder about the long term health issues associated with living inside of a continuously operating, very low power microwave oven. Hmmmm. Make a nice longitudinal study. Volunteers anyone?

The trivial way to fix the issue of getting in trouble after experimenting with transmitters is to get your amateur radio license.

I think people in general misunderstand what the licence is about, the extra frequencies you have access to are incidental, the license is about being able to legally transmit with _homemade_ equipment that does not need external review. That’s why the license exam is about electronics design principles and not just a list of frequency/power limits.

I wonder if the foil backing used on some foam insulation panels as a vapor barrier, though an imperfect Faraday cage since the foil on each panel isn’t electrically joined, is already enough to block radar imaging.

That insulation panel foil does create a lot of problems for cell phone reception and would pretty much shut the thru-wall radar down, as it needs line of sight and so wouldn’t be able to leak out through the windows and roofline.

Like a lot of things in tech, if it is going to work well then some engineering has to go into it.

It has been a long time since I worked with RF (um, some 40 years) but it seems to me that shield thickness is an issue related to wavelength of the scanning RF. Also, if the foil is imperfect (er, holes or lack of coverage) each defect is a potential problem. Faraday cages are not effective against low frequencies and a compass will be affected by the Earth’s field inside of a cage. It may not point N/S but the static or very very low freq field penetrates the cage.

Foil will do something but probably would not be effective against a determined agent with a well designed scanner.

Also, it helps if all the surfaces are electrically connected, have a very low resistance or impedance / reactance, and are well grounded. If a mesh is used, the size of the holes will determine which wavelengths are blocked.

To protect against all wavelengths and defeat any scanning tech then I do believe decent gauge solid metal AL or CU is the ticket. Aluminum is ok but copper is better. Steel is good. Basically buy some sea cans, cut holes for doors etc and weld them together in a pleasing manner to live in. No windows or go and price out high conductivity doped glass panes with multiple layers. In my experience most containers coming here from Asia get piled up or crushed for scrap. I think they would be the most economical way to create a Faraday cage home.

If blocking nuclear weapon created EMPs is part of the criteria then really deep pockets will be a necessary pre-req.

I haven’t looked at this stuff since around 1974 when the company I was with was constructing computerized ATC centres. Lots of concerns about military and civilian radars causing bit flips in the CPUs.

I always wonder if it would be worthwhile to connect that foil electrically and then optionally connect it to ground when installing insulation. It might be becoming a must as time progresses and the maniacal agencies continue to be unchecked but their tech gets more advanced still.

The disadvantage is of course the signals you want to get out and in getting blocked, but you can use an external antenna for some of that..

A recent Supreme Court decision on the use of IR scanning for finding grow rooms, declared that the use of ANY spectrum or device for non-human (five senses) searches requires a valid search warrant.
T-waves, IR, RF, X-rays.
The Faraday shield ain’t a bad idea.
Shelter in place during extreme space weather events, with everything secure even EMP events.

So the switches themselves are pretty damn fast, albeit quite lossy…
Did you get yours through the university or on your own? (will have to look up if there are export restrictions, but might want to buy one)
Do you think it would be feasible to build a 4-bit phase shifter for a passive antenna using this switch or are the losses too great?

You can find integrated RF switches that go to 3GHz for 0.5€/pcs
They might have more atenuation(but not neceserry) than RF relays but I think they more than make up for it in price and speed.http://si.farnell.com/rf_rf-switches

I’m a bit perplexed about all the aluminum scaffolding, they act like that has no effect, the MIT one also seems to use metal screws through the antenna to hold it.although I think the actual supporting L shaped thing might be plastic.. it seems odd though to use metal where they use it.

Given this, would it be possible to integrate the electronics with the antenna board? If so, I’m sure someone has thought of this. Would it be possible to design a phased array using individual antenna elements that combined the antenna design used here with the electronics in this other excellent post, all integrated on one PCB: https://hackaday.com/2014/12/03/extremely-detailed-fmcw-radar-build/ ? I’d guess you’d probably need common timing, although maybe you could recover / compensate for this in software…

I assume that the size of the antennas you’re using here is dictated by the desire for high gain needed to penetrate walls (and receive the tiny amount of attenuated reflected radiation) ? I again assume it might be possible to miniaturize all this, at a lower performance point.

Now from the cursory glance of what I see there and my limited knowledge of antennas I still think it’s odd to put metal screw through it. As for the LNA, that is located at the feedpoint from what I gather and that’s about where you normally expect the LNA to be, but to have metal screws along the edge of the antenna, or metal strips connected through to a scaffolding still seems odd to me. But hey, I’m sure they know a hell of a lot more than I do.

This looks like a time-division multiplexed MIMO radar to me. Could be wrong. Interesting arrangement. Splitting the (I assume) transmitter antenna array as Gregory has done reduces the required separation of the receiver elements to avoid aliasing (drx = Mdtx, where M is the number of elements in an individual transmitter array), so the overall footprint of the array is optimised. However, does this arrangement have minimum redundancy? Some virtual elements might overlap?

Yes, it is TDM MIMO. Although depending on who you talk to others might call it switched array. In the various papers that were written about these systems its been called both TDM MIMO and Switched array. Yes there are more virtual elements but these are not leveraged, I only dial in a subset of 44 elements to achieve a lambda/2 spacing across the 8.5′ aperture. No additional MIMO processing is applied to leverage the virtual elements so i think a good path fwd on this one would be to have someone do exactly that.

You have to admit though that it should have some praise, to do that without prior precedent out of parts meant for something completely different, it’s impressive..
I’ve seen praise put on females into tech for no specific reason, but jeri ellsworth is impressive and would get praise if she was a guy too.

Yeah, that isn’t one. If the garage were able to see through walls, you’d say “which sees through walls”, and even then it’d be tortured grammar. The sentence is perfectly clear, is English your first language?

Greg, I have a question I don’t see you answering in the comments and perhaps tangentally in your article: what about, instead of going the old, expensive way of using one transmitter driving the whole array, you instead use lots of cheap, independent, low-power transmitters like PAVE-PAWS and related radars use that are synchronized in “baseband” (like GPS-slaving Cs/Rb/quartz clocks + control signals from the master computer)?

This is true, active phased arrays are very expensive. Depending to what level each element has independence, eg each one could be an entire small radar by itself or each element is simply a PA, phase shifter, TR, and LNA. Earlier phased array radars only used one phase shifter per element (or per group of say 4 elements or so, known as a sub-array), nothing active. There are different levels of complexity. Basically the more complexity in the element the more the entire system costs. For radar devices these days it continues to be less expensive to use a dish whenever possible. You goto an array for speed, when you must scan faster than a dish. For the radars discussed in this article i traded slower imaging speeds (10-11 Hz) for less complicated elements.

THE NEUROTech. have the Functionings of delivers Airborne Techno–Electromagnetic-Stimulus-Wave in of Vital direct Intrusives STIMULATINGS of Humans BRAIN to acquired the Non-Consensual Conditioned-Sets of ‘BIO-NEURAL-MENTAL’ Effects Outcomes of from any individuals in the city(the Effects-Density to persons depends on stages-conditions and Bio-Physio dependent), via giant Microwave Antenna at for the commercial broadcasting(ALL compass in every spot of the city found Disoriented with degrees, due to the Abnormal EMR Power Effects). And couplings Satellite the Covert Surveillance over peoples most PRIVACY, espionagings individuals Intellectual Properties and Non-Public materials with populations as a whole.

AND in of X-Hi Radiation dispersings in Atmosphere with the hk observatory recorded lowest 1,300 mSv/Hr(65XOver), and the scientific-facts quoted in hk local newspress(Mar.30,2015) proven the Astoundings High Levels of Cancer-Causation Radiation measured in the city in 0.34 – 0.45 mSv/Hr, and is Just 40% Lower than the Japan ‘Abandoned-City’ which near the Fukushima Nuclear Leakages sites measured.

AND the NEUROTransmittings-Waves-Effects of anywhere in effectings Deep LIFE-LIVINGS-FREEDOMS, SAFETIES and HEALTH of complete population in the city, and Extremely Hamperings the Society-Publics Safeties and Orders ALONG with the Energy-Waves in effectings other regions in Pan Asia Pacific and far to Europes &N.America. …….. A bit more info in my Face Book Wall.(Ref.: “US Electromagnetic Weapons And Human Rights”–Global Research ca.).

IN principles, I am the prime ‘Electro-Brain-Interfaces-Targeted’ victims in the city (#TargetedIndividuals), since my ex-girlfriend was succumbed to Suicides by the ‘Electro-Telepathy-GangStalkings’ shortly before I was Fully-Attackings by the perps., as my ex-girlfriend didn’t co-operated with the ‘Electro-Telepathy-GangStalkings’ to sabotages my Business/Life(this was V2k(Voices to Skull Transmissions)PLUS EMR Images Transmittings (Hallucination effects)into my Brains by the ‘Psychotronic Electromagnetic Weapons’ after 2-3 years of the ‘Telepathy-Terrorist-Threats-Torturings, as I believes the ‘Electro-Telepathy-Doers’ Hope to Sadden/Soften or Threatens me to prevent me from disclosings it). OF course I did noticed my ex-girlfriend had some bizarre questions and Stranges-Manner and UnSelf-conditions from time to time before she took her own Life, and of course I can agreed she had no any ideas to how/what to tell me Whats Happenings to her actually.

THE ‘Electro-Telepathy-GangStalkings’ was engaged by one of my business-rivals to act the ‘Subliminal-Controls’ over me for the business interests(it means the ‘Electro-Telepathy-Doers’ started with my ex-girlfriend first with the ‘Sweeties-Plannings’, and ‘Electro-Monitors’ me and her long before we noticed their ‘Telepathy-Psycho-Operationals/works/existences, and they got a lot of personals/privacy details in of the plannings, and used as one of the ‘Torturings-Means’ in later-on. (‘Psychic-Coercives-Tactics’).

THE ‘Electro-Telepathy-StalkingsGang’ got several high rank Detectives as Back-Bone-Runners, and of course the ‘bone-runners’ did also Torturings me quite like no other choices, and to no avails.

AFTERWARDS, few Senior-Top police personnels were ‘Incited’ in to the ‘Telepathy-Mind-Torturings’ psychic-murders-brokerings over me, by the several young girls of the gang by servings the few ‘Greedy’ Top Police-Perverts of erotics Sex-Lust(this was also V2k(voices/ speeches direct Transmittings into humans brain)into my Brains by the ‘Electro-Telepathy-Doers’ since I think they wanted to Pressings/back me-down by sayings as, You got no any chances to get any ways out !!!!).

LATER ON, the few ‘Conscious-Controlled’ Top Police-Man manipulated the job-relationships to have several the city well-known City Councilors sit in and stir up some more and make funs out of me, and asking many as to they Prouded political questions ?????(I told them you knows ‘Gods’ will speakings asks, you Hypocrites-Nobles-Faked here to Fools/Torturings innocents citizens to say the Hell-Hole ‘Political’ !!!!), it was also to my knowing there are several Girls Movies/TV stars/celebrities also presences together to Make Funs/Agitate/ Temptings me Unshamefully, and of course along with the ‘Electro-NEUROTelepathy-Effects’ of inductings various NeuroTransmitters and Brain-functional-State Evokings(as Seratonin with Calm/Peaces/Loves-Cares effects, Dopamine with High Ego/High-Moods, Adrenaline with Arousals/sex counter or Fears, Stress Hormones, and Brain-functional-States manoeuvrings, ………………. ,), and with the girls celebrities Dump-obsesses, its really turns the Atmosphere/ situations in to No-Hells-Worlds, and its really easy to hook any victims into Hysterics/Insanes

IT may also to my knowing that few govt top officials also awared of the Dire Situations but to do no anythings in of the heavily ‘Bureaucratics’ they picked.

NOW, as to my knowing the ‘Electro-Telepathy-GangStalkings’ no longer financed by any peoples, but was given free foods and Meth.(ICE)drugs by the local police drugs, and the ‘Electro-Telepathy-Doers’ never-ended ‘Telepathy-Psychic-Psycho-Torturings’ in of their Self-Joys and Out-Minded Delusionals. (“Evils-Minded Psychopathy-Aberrants !!!!).

EVERYONE can see that no Authorities and Rights Groups will do anythings(even the High-Branded UN Human Rights Office/Amnesty Int’l Offices in the city hk will do little-pit)due to the heavy ‘BUREAUCRACY’ circumstances, till Things ‘Blow-Over’. With hk small city to no few peoples knows and even not willing to see their own Brains are being ‘Zapped-Electrocuted’ by the Weaponry-Technologies in 24hrs-days-years and with next generation also.

I AM now keeping Pressurings on the local police force by writing/x-rox letters to different councilors and govt. salaried officials, and postings more info onto the Internet. WISH Lucks with my side.

I Sincerely thanks to you ALL and Hope you all in Health and Success. Thanks much and thanks again.

He does wish us all health and success (even while our brains are turned to mulch by the telepathy devices). So that’s nice.
There’s something to be said about polite comments that wish other well in the HaD comment sections of today.

This post will self destruct in 10..9..8..(close the tab NOW)..6..5..4….

Chun I can sell you a helmet, or beanie that will block those harmful mind control rays, probably starting at 500 dollars and will be 1000% more fashionable than that tinfoil hat you been wearing. PM me for details.

I believe some anti-schizophrenia medications can alter the functioning of the brain in such a way as it is no longer susceptible to electronic resonances. Ask a doctor to put you on some, a good doctor will be aware of the electronic warfare side, tell him that’s your problem.